In prior art, several routing methods used in ATM networks (Asynchronous Transfer Mode, ATM) are known, such as the PNNI standard (Private Network-Node Interface, PNNI) by ATM Forum and the method presented in patent publication EP 0 814 583A2. Prior-art methods can be divided into two groups. For example, the above-mentioned methods represent shortest-path routing methods, which are derived from the routing methods used in data networks. Their aim is to define the shortest route between two nodes, i.e. e.g. the route with the smallest delay. However, in ATM networks minimising the delay is not of such essential importance as in traditional data networks because the ATM service categories define the scope for the delay.
Another known group of routing methods are the methods based on LLR algorithms (Least Loaded Routing, LLR), which are used in the present-day telephone network. They involve the problem that a direct connection is assumed to exist between all nodes in the network. Moreover, they do not take into account the asymmetry, which is typical of ATM connections. In ATM connections, outgoing traffic is often only a fraction of incoming traffic.
Both methods have the drawback that demanding and time-consuming optimisation calculations have to be carried out in each node of the network. Therefore, the nodes need a large processing capacity and complex software. In addition, complete information about the condition of each link in the network has to be maintained in each node. Collecting this information and keeping it up to date requires a large volume of signalling traffic, thus wasting network resources.